Experimental studies on the correlations of male respiratory parameters with their body composition

Respiratory parameters for various body mass indexes (BMIs) were incompletely reported and only utilized to calculate the metabolic rate. This study aimed to investigate these parameters and their relationships with body composition to identify key factors contributing to inter-individual differences. Thirty-eight healthy males were recruited and categorized into four groups: low-weight (Glw), normal-weight (Gnw), overweight (Gow) and obesity (Gob). Their oxygen uptake, CO₂ emission rates, respiratory quotients, ventilation volumes, metabolic heat production, respiratory heat losses, respiratory rates, body composition and geometric parameters were measured under the three activity conditions, i.e., lying-flat, sitting-still, and intense exercise. Significant body size differences (p < 0.05) and large effect sizes (f = 0.42–1.07) were observed in oxygen uptake, CO₂ emission rate and metabolic heat production. Oxygen uptake and metabolic heat production were positively correlated with muscle mass (r = 0.45–0.74) which has been demonstrated to account for inter-individual differences. A prediction model for muscle mass (Adjusted R² = 0.930) was developed based on body geometric parameters. Furthermore, the lying-flat and sitting-still exhaled air volumes for Chinese men (0.68 kg/h) were underestimated in the predicted mean vote (PMV) model (0.45 kg/h), which resulted in a mean absolute error of over 35 % in respiratory heat loss. We summarized all respiratory parameters for different body sizes across various activities, as shown in the Appendix. These findings contribute fundamental knowledge to establishing respiratory models for Chinese people.